The present invention relates to a pressure sensor diagnosing method that detects the rail pressure in a common rail fuel injection control apparatus, and a common rail fuel injection control apparatus using the same, and in particular, to a pressure sensor diagnosing method and a common rail fuel injection control apparatus capable of detecting a failure of a pressure sensor with a simple configuration and at low cost.
In a so-called common rail fuel injection control apparatus, a pressure sensor is an essential component for detecting an actual rail pressure needed for rail pressure control. Since a failure of the pressure sensor has a major effect on rail pressure control, various diagnosing methods, apparatuses, and the like have been proposed and put into practical use in the related art.
For example, a method referred to as a so-called offset test has been proposed, in which obtains a detection signal of a pressure sensor when it is determined that the fuel pressure of a common rail has been reduced to atmospheric pressure, calculates the fuel pressure corresponding to the detected signal, and determines that the pressure sensor has failed when a difference between the calculated fuel pressure and atmospheric pressure is a predetermined value or more (See, for example, pages 3 to 6 and FIGS. 1 and 2 in JP-A-2007-242332).
Further, other than the offset test, various methods, apparatuses, and the like, which diagnose whether or not a gradient of the pressure sensor is normal, have been proposed and put into practical use.
For example, as a method adopting a configuration in which an electromagnetic type safety valve is provided in the common rail, there is a method that learns an operation characteristic of the electromagnetic type safety valve through a so-called learning process, and determines that the pressure sensor is failed if the range of the learnt value exceeds a predetermined range.
However, in the method disclosed in JP-A-2007-242332, it is possible to perform general diagnosis of whether or not the output of the pressure sensor is normal under atmospheric pressure, but it is not possible to diagnose whether or not the gradient of an output characteristic of the pressure sensor is normal under atmospheric pressure. Therefore, there is a problem in that the method is not able to respond to the demand for diagnosing the gradient of the output characteristic of the pressure sensor.
On the other hand, in the method that learns an operation characteristic of the electromagnetic type safety valve through a so-called learning process and determines that the pressure sensor is failed if a range of the learnt value exceeds a predetermined range, it is assumed that a configuration equipped with an electromagnetic safety valve is adopted. However, an electromagnetic type necessarily should be used as the safety valve. Since there are cases where a mechanical safety valve is used, or cases where a configuration not equipped with a safety valve itself is used, there is a problem in that this method lacks generality as a diagnosing method.